In the mining industry, a favored explosive material comprises ammonium nitrate and fuel oil (commonly known as "ANFO"). This explosive may be used by forming (by drilling or jet piercing) holes ("blast holes") in the ore body, filling the holes with ANFO, and then detonating the explosive. The water which collects in blast holes, either from rain or surface water or from underground sources, has a deleterious affect on ammonium nitrate, and as a result blast holes are commonly lined with a waterproof, plastic liner to keep the water from the explosive. The empty liners are inserted into the blast holes, and the liners are later charged with explosives.
Insertion of blast hole liners into blast holes is ordinarily accomplished by weighting the leading edge of the liner with weighting material, such as may be found at the blast hole site. The weighting material may be inserted into pouches or pockets located in the leading edge of the liner. Blast hole liners of this general type are shown in Canadian Pat. No. 667,051, U.S. Pat. No. 4,019,438 and commonly owned U.S. Pat. Nos. 3,881,417 and 3,760,727. Certain of these liners are quite complex in construction, and accordingly are rather expensive to fabricate. Since it is not practical to test the waterproof qualities of individual blast hole liners before insertion thereof in the blast holes, for safety reasons liner manufacturers tend to make blast hole liners perhaps unnecessarily strong in an effort to assure that the liners will not fail at use, which effort adds to the cost of the liner. Such liners generally are made of tubular plastic stock, and are assembled by means of various cutting and numerous heat seals, as shown, for example, in U.S. Pat. Nos. 3,760,727 and 4,019,438. Certain of such liners are so designed with weight pockets as to transmit stresses incurred upon filling with explosive to an otherwise waterproof tube, the stresses tending to rip the latter or to destroy waterproof seals.
It would be desirable to provide a blast hole liner which could be easily and inexpensively manufactured, which would require few if any cutting procedures for the liner stock, which would require a minimum of heat sealing, and which would reduce the transfer of stresses incurred upon filling the liner with explosive.